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Understanding of degradation mechanisms in batteries is essential for the widespread use of eco-friendly vehicles. Degradation mechanisms affect battery performance not only individually but also in a coupled manner. Solid electrolyte interface (SEI) formation deteriorates battery capacity through consuming available lithium ions. On the other hand, as the SEI layer grows over multiple cycles, the level of mechanical constraints is changed, which can affect the fracture behavior of the active particles. We investigate the effect of the SEI layer growth on the fracture probability of the electrode particles. The simulations show that as the SEI layer grows, tensile stress inside the active particles turns into compressive stress, reducing the probability of particle fracture. Once the SEI layer is fractured, the particle fracture is sequentially more likely to happen because the SEI constraint is removed. The study emphasizes that the stability of SEI layers is important because it helps in alleviating electrochemical performance fade as well as mechanical failure probability. In addition, the SEI layer on small particles tends to be more fractured than that on large particles, suggesting that the particle size uniformity is essential for reducing the fracture probability of the SEI layers at the electrode.

In this study, stress generation at the electrode in Li-ion batteries was studied using a two-dimensional cell-scale model that includes multiple active particles during galvanostatic discharge. Numerical simulations were performed using an electrochemical-mechanical coupled model to elucidate the simultaneous effects of particle size and location, lithium intercalation kinetics and binder constraints on the stress. The simulation results showed that when different sizes of particle are considered in the electrode, the small particles were discharged more than the large particles, resulting in higher level of stress in the smaller particles. In addition, the closer the particles were located to the separator, the larger the stresses that were developed in those particles. Therefore, a layered structure, where the particle size gradually increases as the distance from the particles to the separator decreases, can alleviate stress on the electrode. When binder constraints were considered for the electrode particles, the stress was increased at the anode and alleviated at the cathode upon discharge. This indicates that the effect of mechanical constraints on stress generation in the particles differs in the lithiation and delithiation process.

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The active particle at the electrode of Li-ion batteries is surrounded by other particles and binders. During the lithiation/delithiation process, these surrounding materials mechanically constrain expansion and contraction of the particle. Since electrochemical and mechanical responses mutually influence each other, the constraining condition can finally affect cell performance. In this paper, we investigate the mechanical and electrochemical responses at the particle and cell levels with consideration of the coupling effect of electrochemistry and mechanics. To study the effect of mechanical constraints on cell